Field of the Invention
The present invention relates to a vehicle transmission mounted on a vehicle that moves forward and rearward.
Description of Related Art
Heretofore, there has been known a vehicle that can carry out a low-speed traveling mode where the vehicle is moved forward or rearward at low speed, in addition to a normal traveling mode. In the low-speed traveling mode, the vehicle can be moved forward and rearward with a simple operation of a controller.
In Japanese Patent Application No. 2014-72612, the applicant has proposed a vehicle equipped with DCT (Dual Clutch Transmission) having a main shaft provided with a train of multiple drive gears, and a counter shaft provided with a train of multiple driven gears meshing with the train of drive gears. The main shaft and the counter shaft are arranged parallel to each other.
A main shaft-side sprocket and a counter shaft-side sprocket are respectively provided on the main shaft and the counter shaft in a relatively rotatable manner, and a reverse travel chain is wound around the sprockets.
The main shaft is configured of a main shaft-inner shaft including the main shaft-side sprocket, and a main shaft-outer shaft arranged coaxially with and radially outward of the main shaft-inner shaft. The main shaft-outer shaft can rotate integrally with or separate from the main shaft-side sprocket arranged on the main shaft-inner shaft. Additionally, a first clutch and a second clutch, which connect and disconnect an engine and a transmission, are provided respectively on one end sides of the main shaft-inner shaft and the main shaft-outer shaft.
In the above-described vehicle transmission, the vehicle cannot move forward or rearward if it is in the neutral state, i.e., if the clutches are disconnected. However, since there is residual oil in the clutches, clutch capacity is generated by the residual oil even when the clutches are disconnected. Hence, the clutches are connected spuriously, so that the main shaft-inner shaft and the main shaft-outer shaft may be rotated slightly by an output-side plate.
As a result, when each of the main shaft-inner shaft and the main shaft-outer shaft is rotating at 1000 rpm, for example, rotation of the main shaft-inner shaft is transmitted in the order of: the main shaft-inner shaft, drive gear for first gear, driven gear for first gear, counter shaft-side sprocket, reverse travel chain, and main shaft-side sprocket. In this case, if the gear ratio between the drive gear for first gear and the driven gear for first gear is 2, and the gear ratio between the sprockets is 1, the main shaft-side sprocket rotates at 500 rpm in the opposite direction of the main shaft-inner shaft and main shaft-outer shaft (−500 rpm).
That is, the difference of rotational speed between the main shaft-side sprocket, and the main shaft-inner shaft and main shaft-outer shaft is 1500 rpm (1000 rpm−(−500 rpm)=1500 rpm).
Accordingly, if the vehicle is to be moved forward or rearward at low speed by engaging the main shaft-outer shaft with the main shaft-side sprocket and causing them to rotate integrally in a low-speed traveling mode, the main shaft-side sprocket and the main shaft-outer shaft need to be engaged with a difference of rotational speed of 1500 rpm. This enlarges the shock at the time of engaging of the main shaft-side sprocket and the main shaft-outer shaft, and the shock makes a large noise.